1. Field of the Invention
The present invention relates to a device that reduces power transmission insulator flashover by preventing the buildup of contaminants and dust on the surface of insulators. More specifically, the present invention is a flashover prevention device for power transmission insulators that creates an envelope of positive and negative ions that covers the insulators' skirts and consequently repels dust and other particles.
2. Description of Related Art
High tension AC power lines typically are suspended from metal towers by insulators comprising a series of insulating skirts (also known as dishes, discs, sheds or shells). Contaminants and dust that accumulate on these skirts reduce the electrical resistance of the insulators, thereby increasing the probability of electrical current flow known as flashover. These contaminants may be generated by salt water, road salt, saltflats, desert dusts, petrochemical industries, etc., and may be transported to the surface of the insulator by gravity, electrostatic attraction, migration of high-permittivity particles into regions of large electric fields, evaporation of solutions and wind. When these materials are deposited on the insulator surface, they behave as a highly variable resistor that tends to be unstable in the presence of electric fields. The leakage current through this resistance causes heat, electrochemical reactions, discharges and flashover.
When this occurs, the ability of the insulator to resist flashover is primarily determined by: the shape of the insulator; the attitude of the insulator (vertical, inclined or horizontal); the properties of the surface of the insulator (hydrophobicity, roughness, surface free energy); and the stickiness or strength of adhesion to contaminants (thereby increasing the insulator's ability to become moist and a tendency to become polluted). The flashover voltage of a polluted insulator depends upon the amount and nature of the pollutants. The degree of pollution by conductive materials is usually estimated by the equivalent salt deposit density (ESDD). Generally, flashover voltage of a polluted insulator is inversely proportional to about 1/5 the power of ESDD in AC systems and 1/3 the power of ESDD in DC systems. Pollutants also contain non-conductive or insoluble materials, measured by the non-soluble material deposit density (NSDD). These materials must be considered in that they affect retention of water, and the ability of the conductive materials to be washed away by dew, fog, rain, etc.
In addition to ESDD and NSDD, flashover voltage characteristics are influenced by wetting of the insulator surface. When a polluted insulator is dry, its flashover voltage level is similar to the level of a clean and dry insulator. The chance of flashover is increased when the wetting is caused by fog, humidity or light rain, because in heavier wetting the pollutant may tend to be washed away. As the surface insulation resistance is lowered, leakage current flows along the surface forming "dry bands". The formation of "dry bands" results in a non-uniform potential distribution that eventually leads to flashover.
Several related art devices have been developed to reduce the accumulation of contaminants on these insulators. One such device consists of the use of an oil bath open to the atmosphere. This technique had to be abandoned, however, because of the deterioration and splashing away of the oil itself. U.S. Pat. No. 3,963,858, issued on Jun. 15, 1976 to Tsen-Chung Cheng et al., describes flashover prevention means for high voltage insulators comprising discrete conductive regions which intercept an electrical arc. U.S. Pat. No. 4,010,316, issued on Mar. 1, 1977 to David C. Jolly et al., describes a high voltage electrical insulator which uses magnetic elements to prevent flashover by deflecting the flashover using a magnetic current. U.S. Pat. No. 4,125,742, issued on Nov. 14, 1978 to Mario Rabinowitz, discusses preventing flashover in tiered insulators by optimizing the relationship between core diameter, tier separation, free path length and total path length between the outer surface and inner core. It should be noted that ionization and ion generating are not disclosed or suggested in any of these references.
U.S. Pat. No. 4,364,752, issued on Dec. 21, 1982 to Richard A. Fitch et al., U.S. Pat. No. 4,539,022, issued on Sep. 3, 1985 to Joseph R. McLoughlin, U.S. Pat. No. 4,944,778, issued on Jul. 31, 1990 to Motoo Yanagawa, and U.S. Pat. No. 5,141,529, issued on Aug. 25, 1992 to Clive C. Oakley et al., all describe various methods and devices for removing particles from gaseous mediums using ionization. The use of these devices to repel particles or dust from electrical insulators is not disclosed or suggested by any of these references. In fact, the large size and/or collection methods used by these devices precludes their use on power line insulators.
Thus, there exists a need for an insulator device for use on high tension AC power lines that prevents the accumulation of particulate contaminants to reduce the likelihood of a flashover event.
None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed.